The present invention relates to the use of image processing and printing.
In a scanning inkjet printer, an inkjet printhead mounted to a carriage moves back and forth across a media. The printhead and carriage assembly is typically guided across the media using one or more carriage guide bars to keep the printhead and carriage assembly properly aligned. During each pass of the printhead and carriage, a control device selectively activates one or more drop generators to eject ink droplets from nozzles in the inkjet printhead and deposit them on the underlying media forming text characters and images.
To print accurately and at higher resolutions, it is important to keep various parts of the inkjet printhead and carriage properly aligned. In particular, the printhead and carriage often experience a rotation about the z-axis perpendicular to the carriage direction due to imperfections in the carriage guide bars. In a large format printer, the printhead and carriage is typically guided by at least two such carriage guide bars. Nonetheless, even two such carriage guide bars are not sufficient to prevent small rotations by the printhead and carriage about the z-axis (the theta-z) direction. While the rotations in the printhead and carriage assembly are reduced, they still are sufficient to create undesirable and noticeable artifacts when printing.
Conventional solutions used to address printhead rotation and other printer alignment issues involve printing and scanning specialized marks. Typically, a specialized mark is developed for each of alignment problem being addressed. In the case of the printhead rotation described above, a specialized mark would be developed to detect the degree of printhead rotation in a given inkjet printer. In a separate calibration operation this specialized mark is then printed in a first pass on a media and then, on a second pass, the relative position of the specialized mark is detected for later analysis and correction of printer detects using either a scanning device built into the inkjet or other types of feedback mechanisms.
These conventional solutions for detecting and correcting the printhead and carriage rotation have several drawbacks. Printing and scanning these marks takes a great deal of time as the mark must first be printed and then later be scanned on separate passes of the inkjet printer. Even if performed properly, alignment performed using these marks is a singular event that generally occurs between print jobs, printhead replacement and other events. Environmental and operational factors that also affect alignment include varying environmental conditions of temperature and humidity as well as changes in the lubrication of the printer, friction, and overall printer usage.
Unfortunately, the dynamic changes in the printhead and carriage rotation are not adequately addressed using the static conventional alignment detection methods. As a consequence, compensating for printhead rotation is limited to information collected at the time of calibration rather than the moment changes in the printer or printer environment occur. Even if it were possible, it is not cost effective to use these conventional methods as frequently as necessary; it would also result in a great deal of wasted media. Accordingly, there is a need to improve the detection of printhead rotation in the theta-z direction if more optimal printed output is desired.
Like reference numbers and designations in the various drawings indicate like elements.